2 Chapter 1 Greater India

The University of Sydney, PhD Thesis, Ana Gibbons, 2012 – Chapter 1 – Greater India and West Australia

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Chapter 1 - Constraining the Jurassic extent of Greater India: tectonic evolution of

the West Australian margin


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ABSTRACT

Alternative reconstructions of the Jurassic northern extent of Greater India differ by up

to several thousand kilometres. We present a new model that is constrained by revised

seafloor spreading anomalies, fracture zones and crustal ages based on drill

sites/dredges from all the abyssal plains along the West Australian margin and the

Wharton Basin, where an unexpected sliver of Jurassic seafloor (153 Ma) has been

found embedded in Cretaceous (95 My-old) seafloor. Based on fracture zone

trajectories, this NeoTethyan sliver must have originally formed along a western

extension of the spreading centre that formed the Argo Abyssal Plain, separating a

western extension of West Argoland/West Burma from Greater India as a ribbon

terrane. The NeoTethyan sliver, Zenith and Wallaby plateaus moved as part of Greater

India until westward ridge jumps isolated them. Following another spreading

reorganisation, the Jurassic crust resumed migrating with Greater India until it was re-

attached to the Australian plate ~95 Ma. The new Wharton Basin data and kinematic

model place strong constraints on the disputed northern Jurassic extent of Greater India.

Late Jurassic seafloor spreading must have reached south to the Cuvier abyssal plain on

the West Australian margin, connected to a spreading ridge wrapping around northern

Greater India, but this Jurassic crust is no longer preserved there, having been entirely

transferred to the conjugate plate by ridge propagations. This discovery constrains the

major portion of Greater India to have been located south of the large-offset Wallaby-

Zenith Fracture Zone, excluding much larger previously proposed shapes of Greater

India.


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INTRODUCTION

The original, pre-collision extent of India’s northern margin, known as Greater India,

continues to be poorly constrained despite the many papers written on this topic. Greater

India was part of East Gondwana until the Early Cretaceous. East Gondwana,

comprising India, Africa, Madagascar, Sri Lanka, Australia, Antarctica and other micro-

continents, had a northern margin that was moulded by several major rifting events that

led to the formation of a succession of ancient ocean basins. The PaleoTethys bounded

this margin from the Middle/Late Devonian until the rifting and northward motion of

the Cimmerian Continent in the Early Permian (Metcalfe, 1996). The eventual collision

of Cimmeria led to the subduction of the entire PaleoTethys by the Late Permian. The

cycle was repeated with the MesoTethys following rifting and subsequent collision of

the Lhasa Block in the Late Triassic and Late Jurassic, respectively (Metcalfe, 1996).

Greater India’s northern margin stretching from Africa to East Timor, was finally

formed by Late Jurassic rifting of Argoland (also referred to as the West Burma Block),

shortly before Greater India’s westward migration commenced (Metcalfe, 1996). Most

tectonic models reconstructing East Gondwana breakup feature Greater India, as a

single block, rifting from the West Australian margin (Fig. 1.1). Yet, the estimated

extents for Greater India vary greatly with many different techniques used to constrain

its extent. A thorough summary of the alternative published models is provided by Ali

and Aitchison (2005). We include a short overview and table 1.1 to highlight these

discrepancies.

Seismic data show that the Himalayas are composed of stacked continental crust (Searle

et al., 1987) approximately 75-80 km thick (Hirn, 1988; Li et al., 2009; Teng, 1987),


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while the Indian crust south of the Himalayas is only about 35 km thick (Zhang et al.,

2007). Models that derive crustal shortening estimates from balancing lithological cross-

sections from the India-Eurasian collision zone, between Himalaya and Tibet, often

result in the smallest estimates for the extent of Greater India, such as 500 km

(Ratschbacher et al., 1994). More crustal shortening is accommodated laterally, into

China (Wang et al., 2001). A pre-collision Greater India extent of only 500 km matches

poorly with the West Australian margin bathymetry as Greater India would not have

reached beyond the Naturaliste Plateau on the southwest edge of Australia (NP, Fig.

1.1), implying that there was no continental crust conjugate to the majority of the West

Australian margin.

Another approach to constrain Greater India’s extent is to look at the timing of collision

between Greater India and Eurasia, but a lack of consensus on this timing has led to a

diverse range of estimated extents. Estimates for the onset of India-Eurasia collision

range from 35 Ma (e.g. Aitchison et al., 2007; Aitchison and Davis, 2004), to 70 Ma

(e.g. Ding et al., 2005; Shi et al., 1996; Willems et al., 1996; Yin and Harrison, 2000).

The proposed 35 Ma collision is based on two distinct collision events: the collision of

an intra-oceanic island-arc with the Eurasian margin around 60-55 Ma (e.g. Acton,

1999; Klootwijk et al., 1991) and the collision of Greater India and Eurasia around 40-

35 Ma (e.g. Patriat and Achache, 1984; Searle et al., 1987). Some proponents of the 70

Ma collision also acknowledge this intra-oceanic arc may have contributed as the earlier

collision (Ding et al., 2005). Changes in convergence rates between India and Eurasia

can also help constrain the timing of their collision (e.g. McKenzie and Sclater, 1971;

Norton and Sclater, 1979; Schlich, 1982; Sclater and Fisher, 1974). Most studies agree

this took place at 50-55 Ma (e.g. Besse and Courtillot, 2002; Molnar and Tapponnier,


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1975; Patriat and Achache, 1984; Torsvik et al., 2008). A more recent study using

seafloor spreading and plate circuits identified an initial slowdown in India-Eurasia

convergence from around 52 Ma, with a sharper drop at 42 Ma (Cande and Stegman,

2011). A 35 Ma collision requires a Greater Indian extent of ~1200 km, reaching the

Wallaby-Zenith Fracture Zone (WZFZ, Fig. 1.1), while a 55 Ma collision requires a

~2000 km Greater Indian extent, reaching the northern tip of the Exmouth Plateau (EP,

Fig. 1.1), but an extent of ~4000 km would be required for the 70 Ma collision, reaching

well beyond East Gondwana in a Mesozoic reconstruction. The 70 Ma collision

therefore could not have been Greater India but might have been another Gondwana-

derived tectonic block, such as the western extent of Argoland, which rifted from

Gondwana in the Late Jurassic (Heine and Müller, 2005).

Paleomagnetic studies combined with apparent polar wonder paths can show when and

by how much terranes migrated following tectonic events, but the results pertinent to

our study encompass a broad range. For instance, paleomagnetic data from the

Linzizong volcanics (from the Lhasa Block in Southern Tibet) show that the India-

Eurasia collision occurred between 64-44 Ma (Chen et al., 2010), but that the onset of

collision was at 53-49 ± 6 Ma (Liebke et al., 2010), or 46 ± 8 Ma, the latter producing a

total convergence of 2900 km ± 1200 km (Dupont-Nivet et al., 2010). Sun et al. (2010),

argue for a 55 Ma onset of collision resulting in an India-Eurasia combined shortening

of 3400 ± 1150 km, while Tan et al. (2010) date the onset of collision to 43 Ma,

implying a total of ~2000 km of convergence. A Greater Indian extent of 3400 km

would reach well over 500 km beyond the Exmouth Plateau in a Mesozoic Gondwana

reconstruction while 2000 km would reach just into the Exmouth Plateau. Klootwijk et

al. (1992) suggested a distinct reduction in India’s northward motion before 55 Ma


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based on paleomagnetic data in the Ninetyeast Ridge. Combining this with a

comparison between north Indian margin paleolatitudes and collision-induced

secondary magnetisations, they defined a minimal Greater India extent reaching 1120

km from the Indian-Himalayan main boundary thrust (MBT), which includes 470 km of

cumulative crustal shortening across the Himalayas. This minimal extent of Greater

India would have reached the WZFZ. Within comparison, van Hinsbergen et al. (2011)

suggest a vast Greater Indian extent based on continental collision at 50 Ma and 650-

1050 km of intra-Asian shortening (north of the Himalayas), necessitating subduction of

extensively thinned continental crust for a prolonged period of time. An even greater

extent for Greater India has been proposed by Johnson (2002), who summarised existing

magnetic anomaly, paleomagnetic and volumetric balancing studies, finding that the

total convergence between India and Eurasia was 1800-2100 km in the west, 2475 km in

the centre and 2750-2800 km in the east, which outlines a wedge-shaped Greater India

that reached over 500 km beyond the northern tip of the Exmouth Plateau.

Another way to constrain the extent of Greater India is to use the morphology of the

Western Australian margin. The relatively undeformed morphology of the ocean basins

along the West Australian margin offers an abundance of constraints to apply to the

problem of Greater India, such as the Cape Range and Wallaby-Zenith Fracture Zones

or continental fragments such as the Wallaby and Naturaliste Plateaus (Fig. 1.1). In the

context of a reconstructed Mesozoic East Gondwana reconstruction, Ali and Aitchison

(2005) proposed that Greater India must have reached to the WZFZ, the equivalent of at

least 950 km north of where the Himalayas currently meet India. Lee and Lawver

(1995) also used West Australian bathymetry to propose that Greater India originally

reached the northern tip of the Exmouth Plateau. Even using a combined approach can


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result in different estimates for Greater India. For instance, Powell et al. (1988), using

bathymetric and palaeomagnetic data, as well as Tibetan underplating, proposed a

Greater India extent of 1500 km, extending roughly to the Cape Range Fracture Zone

(CRFZ, Fig. 1.1). Yet, no studies have attempted to combine the morphological

evidence offshore West Australia with a regionally-constrained plate tectonic model.


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Figure 1.1. The Sandwell and Smith (2009) 1-degree satellite-derived free-air gravity

along the West Australian margin showing the location of the Argo Abyssal Plain

(AAP), Gascoyne Abyssal Plain (GAP), Cuvier Abyssal Plain (CAP), Perth Abyssal

Plain (PAP), Exmouth Plateau (EP), Rankin Trend (RT), Naturaliste Plateau (NP),

Wallaby Plateau (WP), Zenith Plateau (ZP), Batavia Knoll (BK), Gulden Draak Knoll

(GDK), Wallaby-Zenith Fracture Zone (WZFZ), Cape Range Fracture Zone (CRFZ),

Dirk Hartog Ridge (DHR), Galah Rise (GR), Investigator Ridge (IR), Lost Dutchmen

Ridge (LDR), Joey Rise (JR), Roo Rise (RR), Sonne Ridge (Sn), Sonja Ridge (Sj),

Investigator Ridge (IR), Broken Ridge and the Wharton Basin. Inverted black triangles

show positions of the CHRISP 2008 seamount dredge samples. Area shown in the black

box is the location of the CHRISP 2008 Jurassic oceanic crust, zoomed in for Fig. 1b.

The West Australian margin formed through two distinct phases, yet studies have

predominantly focussed on subsets of the margin and no model for the formation of the

entire West Australian margin has been attempted. Existing tectonic interpretations of

subsets of the margin have resulted in conflicting tectonic models both within and

between the West Australian abyssal plains (Fig. 1.1). Conflicts include the presence or

absence of ridge jumps in the Argo Abyssal Plain and alternative Jurassic versus Early

Cretaceous magnetic anomalies in the Gascoyne Abyssal Plain (Heine and Müller,

2005; Robb et al., 2005; Sager et al., 1992). A further complication is that most of these

abyssal plains formed adjacent to volcanic margins, resulting in the masking of seafloor

spreading magnetic anomalies by widespread excess volcanism. The West Australian

margin is also characterized by many complex structural features, which form narrow,

linear gravity anomalies and discontinuities within the magnetic lineations, and many

are due to numerous ridge propagation events, adding to the complexity of the margin,


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though these features can also give clues as to the margin’s formation. Understanding

the temporal and spatial evolution of all the West Australian abyssal plains is crucial for

accurately constraining the extent and kinematic history of Greater India and other

blocks that rifted from the West Australian margin. Considering both local and regional

constraints, we build a tectonic reconstruction for the separation of Australia and India

that satisfies all the available constraints along this margin and fully links the Jurassic

and Cretaceous spreading episodes. We develop a dynamic, continuous plate tectonic

model for the formation of the West Australian Abyssal Plains by integrating (i)

recently collected magnetic shiptrack data with existing magnetic datasets, (ii) our

interpretations of fracture zones, pseudofaults (age discontinuities from ridge jumps),

extinct ridges and microcontinental rafts, and (iii) regional plate tectonic constraints

from the neighbouring Gondwana-derived continental blocks and local microblocks.

Greater Indian estimates

Reach along West Australian margin (WAM)

Evidence Reference Pro’s/Con’s

500 km Tip of Naturaliste Plateau

Crustal shortening estimates

(Ratschbacher et al., 1994)

No conjugate to most of West Australia

1200 km Wallaby-Zenith Fracture Zone

~35 Ma collision and WAM morphology

(e.g. Aitchison et al., 2007; Aitchison and Davis, 2004)

No conjugate for the Exmouth Plateau

2000 km Tip of Exmouth Plateau

~55 Ma collision (e.g. Acton, 1999; Klootwijk et al., 1991)

Good match to WAM

4000 km Well beyond northern Australia (Mesozoic Gondwana northern margin)

~70 Ma collision (e.g. Ding et al., 2005; Shi et al., 1996; Willems et al., 1996; Yin and Harrison, 2000)

The Jurassic Argo abyssal plain could not have formed because…

2900 km ± 1200 km

Beyond tip of Exmouth Plateau

46 ± 8 Ma collision from paleomagnetism

(Dupont-Nivet et al., 2010)

Greater India reached beyond Argoland

3400 ± 1150 km

Beyond tip of Exmouth Plateau

~55 Ma collision, paleomagnetism

Sun et al., (2010) Too big (as above)


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2000 km Tip of Exmouth Plateau

~43 Ma collision, paleomagnetism

Tan et al., (2010) Good match

1120 km Almost to the Wallaby-Zenith FZ

Reduced plate motion ~55 Ma, paleomagnetism

Klootwijk et al., (1992)

No conjugate for Exmouth Plateau

1800-2800 km

Wedge-shaped Greater India reaching beyond East Gondwana (wider in the east)

Magnetic anomalies, paleomagnetism, volumetric balancing

Johnson (2002) Too big for WAM (beyond the Jurassic Argo Abyssal Plain)

1500 km To Cape Range FZ Bathymetry and paleomagnetism

Powell et al., (1988)

No conjugate for the Exmouth Plateau

Table 1.1. Summary of previously proposed extents for Greater India, including

comparisons with our Mesozoic Gondwana reconstruction.

GEOLOGICAL SETTING AND PREVIOUS WORK

The West Australian margin and its adjacent abyssal plains make up the

physiogeography of the eastern Indian Ocean (Heezen and Tharp, 1965). This passive

margin runs from the Java-Sunda subduction zone in the north to Broken Ridge in the

south and includes the Argo, Gascoyne, Cuvier and Perth Abyssal Plains (Fig. 1.1).

Much of the conjugate seafloor located offshore Greater India has now been consumed

by subduction/collision beneath Eurasia and Southeast Asia. The remaining seafloor

offshore Western Australia is riddled with tectonic anomalies such as seamounts,

volcanic plateaus and continental rafts.

The Argo Abyssal Plain, at roughly 600 km across and 5.7 km deep, is situated at the

northern tip of the West Australian margin. It is an almost featureless expanse of old

ocean floor bordered by submerged continental horsts, grabens and half-grabens from


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the Exmouth Plateau (west) to the Scott Plateau (east), and bounded to the north by the

Java-Sunda subduction zone (Falvey and Veevers, 1974). Formation of Argo seafloor

was initially compartmentalised between several northwest-trending fracture zones,

accommodating the curved margin (Fig. 1.2a-b). Most studies agree on the presence of

several fracture zones with dextral offsets in the west, and greater sinistral offsets in the

east, (Fullerton et al., 1989; Heine and Müller, 2005; Heirtzler et al., 1978; Powell and

Luyendyk, 1982). The exact locations of fracture zones vary between studies and have

been inferred mainly on the basis of magnetic anomaly offsets.


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Figure 1.2: Comparison of previous magnetic anomaly, fracture zone and continent-

ocean boundary (COB) interpretations of the Abyssal Plains offshore Western Australia,

overlain on 1-degree satellite-derived free-air gravity (Sandwell and Smith, 2009) for

the Argo, Gascoyne and Cuvier Abyssal Plains: (a) Fullerton et al., 1989; (b), Heine and

Müller, 2005; (c), Robb et al., 2005; and Perth Abyssal Plain: (d) Markl 1974. Red

dashed lines indicate fracture zones, black lines indicate isochrons, purple dashed lines

indicate COB, black and white lines indicate pseudofaults (PF), yellow lines indicate

extinct ridges (ER). Isochrons are identified in black lettering.

Cenozoic magnetic anomalies C32-C24 (71-52 Ma), were initially identified in the Argo

Abyssal Plain trending at 60° (Falvey, 1972), but they were revised to the Mesozoic

after ODP Site 261 revealed a basement age of 152 Ma (Heirtzler et al., 1978; Veevers

et al., 1974). The first study to link the Argo spreading system to those to the southwest

proposed a southward ridge jump in only the western Argo at 136 Ma (essentially over

the Joey Rise), forming a triple junction, though this resulted in a large offset between

the Argo and Gascoyne anomalies (Powell and Luyendyk, 1982). Following the

acquisition of new aeromagnetic data, Fullerton et. al., (1989), identified chrons M25-

M15 (155-138 Ma, Fig. 1.2a), as a continuous sequence throughout the Argo Abyssal

Plain. Heine and Müller (2005) proposed a southward ridge jump at 136 Ma (chron

M14) over the north Argo Abyssal Plain, identifying a pseudofault following a high-

amplitude (-500nT) magnetic anomaly and prominent positive gravity anomaly near the

Sunda Rise. They also linked the Argo to the Gascoyne by extending the Argo Jurassic

anomalies M25-M22A around the Exmouth Plateau, juxtaposing them with anomalies

M6-M0 along a pseudofault that is not visible in the marine gravity grid (Fig. 1.2b).


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Marking the western limit of the Argo Abyssal Plain is the Joey Rise, a set of almost

equally spaced volcanic ridges splaying north from the northwest tip of the Exmouth

Plateau, a platform of stretched and intruded continental crust composed of northeast-

oriented, subsided segments (Falvey and Veevers, 1974). The Exmouth Plateau marks

the eastern boundary of the Gascoyne Abyssal Plain, another smooth expanse of old

ocean floor with some seamounts in the north and a volcanic complex underlying the

Galah Rise further east (Rey et al., 2008). Fullerton et. al. (1989) identified conjugate

anomalies M10-M4 (130-127 Ma) reflected about an extinct ridge, with curving fracture

zones to account for the converging younger anomalies M4-M0 (126-120 Ma) further

west (Fig. 1.2a). This convergence is better explained by Robb et al. (2005), who

proposed a dominant southward propagating ridge, originating west of the Joey Rise,

that trapped conjugate anomalies M4-M2 (126-124 Ma), as the spreading centre

propagated south (Fig. 1.2c). This interpretation abandoned the conjugate series in the

eastern Gascoyne and did not attempt to link it with the Argo spreading system, having

not extended their study to that area. The Cape Range Fracture Zone (CRFZ), at the

southern end of the Exmouth Plateau, marks the north of the Cuvier Abyssal Plain,

which contains two north-striking linear features: the Sonne and Sonja Ridges (Fig. 1.1).

The Sonne Ridge is interpreted as an extinct spreading centre reflecting anomalies M11-

M5 (132-127 Ma) about its axis, while the Sonja Ridge is a pseudofault resulting from

the westward ridge jump (Mihut and Müller, 1998). Other magnetic anomaly studies

had similar results identifying conjugate anomalies M10-M5 (130-127 Ma) about the

Sonne Ridge and chron M4 as the oldest anomaly in the southern Gascoyne following a

westward ridge jump (Fullerton et al., 1989; Robb et al., 2005; Sager et al., 1992). Only

Robb et al., (2005), identified both the Sonja and Sonne as extinct ridges, resulting from

a duelling ridge scenario with anomalies M4-M6 and M10-M5 about their respective


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axes. Further south, the Zenith and Wallaby Plateaus comprise the southern portions of

the Gascoyne and Cuvier Abyssal Plains, respectively. Dredging between the Wallaby

Plateau and the margin yielded tholeiitic basalts (von Stackelberg et al., 1980), a

product of oceanic ridges. Only one study identified magnetic anomalies M14-M11

(136-132 Ma), east of the Wallaby Plateau (Mihut and Muller, 1998). Seismic studies of

the Wallaby Plateau suggest a non-volcanic basement core modified by magma from

seafloor spreading (Borissova, 2002). Planke et al., (2002), reviewing seismic and

dredge data, proposed that both the Wallaby and Zenith Plateaus have continental cores

that were intruded by magmatic rocks emplaced by rift propagation events during the

breakup. More evidence of continental material was presented by Nelson et al., (2009)

who reported that dredge samples, south of the Wallaby Plateau, included volcanic

rocks showing variability in their silica content, as well as several terrigenous clastic,

fossil-rich rocks, which were likely deposited when a portion of the plateau was near or

above sea-level. Fossil assemblages dredged from the southern plateau, including

Oxfordian-Kimmeridgian foraminifera, date to between the Late Berriasian to

Berremian-Aptian, suggesting a pre-breakup sedimentary section exists (Stilwell et al.,

2012).

The Gascoyne and Cuvier Abyssal Plains, and their plateaus, are terminated to the south

by the 2000 km-long Wallaby-Zenith Fracture Zone (WZFZ), which has an unusually

large width (~200 km) and is composed of several smaller offset ridges oriented at acute

angles to its southern edge (Nelson et al., 2009). The WZFZ marks the northern limit of

the Perth Abyssal Plain, within which there are several major tectonic features,

including the Naturaliste Plateau, Lost Dutchmen Ridge, Dirk Hartog Ridge, and the

Batavia and Gulden Draak Knolls (Fig. 1.1). The Naturaliste Plateau, next to the


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southernmost portion of the West Australian margin, has been identified as stretched

continental crust with intrusions from seafloor spreading (Symonds et al., 1998).

Samples from the Naturaliste Plateau contain reworked Mesoproterozoic crust with

affinities to the Albany-Fraser-Wilkes orogenic rocks of Australia and Antarctica

(Halpin et al., 2008). The crustal nature of the other anomalous features still remains

unclear due to a lack of investigation. The magnetic anomalies in the Perth Abyssal

Plain have been interpreted as M11-M0 (132-120 Ma), with M4-M0 (126-120 Ma)

offset dextrally southwest of the Naturaliste Plateau (Johnson et al., 1980; Markl, 1974,

1978; Veevers et al., 1991), Fig. 1.2d. The remainder of the Perth Abyssal Plain was

created during the Cretaceous Normal Superchron (CNS). The Wharton Basin,

northwest of the Zenith Plateau, contains a remarkable set of curved fracture zones (Fig.

1.1), which have been linked to the 100 Ma spreading reorganisation when the Indian

Ocean’s seafloor spreading ridges were realigned from trending 20 degrees to 90

degrees, so that Greater India could migrate north (Müller et al., 2000; Veevers, 2000).

These curved fracture zones have yet to be replicated in a tectonic model.

METHODOLOGY AND DATA

We formulate a new plate tectonic model for the breakup and early spreading history

between India and Australia using the oceanic crust offshore the West Australian

margin. This area provides numerous constraints, such as seafloor spreading magnetic

anomalies, fracture zones, extinct spreading ridges, pseudofaults, oceanic plateaus and

seamounts, with which we can define our tectonic blocks and their migration. We use

the satellite-derived gravity anomaly grid of (Sandwell and Smith, 2009) to interpret

fracture zones and features formed as a result of spreading reconfigurations, such as


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extinct ridges and pseudofaults (a raised ‘step’ in the seafloor where a new ridge began

forming in older oceanic crust). Pseudofaults are visible as subtle differences in gravity

and magnetic anomaly strength between areas of the ocean floor, while extinct ridges

can appear as linear features and/or give an axis of symmetry in the magnetic anomalies.

Fracture zones are perceptible as linear negative gravity anomaly features. We also

identify areas of anomalous oceanic crust, which may be volcanic features or

continental rafts.

Tectonic outlines and micro-blocks

The Naturaliste, Wallaby and Zenith Plateaus, and Gulden Draak and Batavia knolls

(Fig. 1.1), may have been micro-continental blocks transferred to the Australian plate

during separate ridge jumps. The Wallaby Plateau was recently found to have a pre-

breakup sedimentary section (Stilwell et al., 2012), suggesting continental affinities,

while the Zenith Plateau appears a good fit to the western outline of the Wallaby but has

yet to be investigated. The Naturaliste Plateau has been identified as stretched

continental crust with intrusions from seafloor spreading (Borissova, 2002). We test

their fit in a Mesozoic reconstruction and define their boundaries using features

identified in the marine gravity grid. We take the WZFZ as the southern limit of the

Zenith and Wallaby Plateaus, and the CRFZ and Sonne ridge for the northern and

eastern limits of the Wallaby Plateau, respectively. The Wallaby Plateau’s western limit

is constrained by the location of the oldest magnetic anomalies we identify in the

southern Gascoyne Abyssal Plain. Batavia and Gulden Draak Knolls, if continental

rafts, would have originally abutted the Naturaliste Plateau, given the fracture zone

constraints, while Greater India’s eastern margin would have remained juxtaposed to the


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west side of the Knolls, until their transferral to the Australian plate several million

years later. We identify the linear feature running west of the Knolls as a pseudofault

resulting from this transferral. Where there are no other constraints available, we pick

the COB using anomaly contrasts in the marine gravity grid (e.g. Naturaliste, Zenith,

East Knolls). We outline Australia’s northwest continent-ocean boundary (COB)

according to published interpretations north (Borissova, 2002; Müller et al., 2005), and

south (Brown et al., 2003), of the WZFZ (dashed line Fig. 1.5).

Seafloor spreading magnetic anomalies

We analyse GEODAS (Geophysical Data System) data from of the National

Geophysical Data Centre (NGDC), and new magnetic profiles acquired during the

August-September 2008 IFM-Geomar CHRISP research cruise. All magnetic shiptrack

data were smoothed by highpass (300 km) and lowpass (10 km) filters to remove

electromagnetic disturbances and noise. We make magnetic anomaly identifications for

the Argo, Gascoyne, Cuvier and Perth Abyssal Plains by comparing magnetic anomalies

from selected ship-track profiles against a synthetic model of seafloor spreading created

using Modmag (Mendel et al., 2005). Table 1.2outlines the parameters used for the

synthetic models. We use the combined timescale of Cande and Kent (1995) and

Gradstein et al. (1994). We pick the young end of the normal polarity for Mesozoic

magnetic anomalies: 26 (155 Ma), 25 (154.1 Ma), 24B (153.5 Ma), 24 (152.1 Ma), 23

(150.7 Ma), 22A (150.4 Ma), 22 (148.1 Ma), 21 (146.7 Ma), 12A (135 Ma), 11A (133.3

Ma), 11 (132.1 Ma), 10N (130.8 Ma), 10 (130.2 Ma), 9 (129.5 Ma), 8 (128.9 Ma), 6

(128.2 Ma), 4 (126.7 Ma), 2 (124 Ma), 0 (120 Ma). See Fig. 4 for the stacked plots of


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our interpretation of selected tracks compared to our synthetic model for each abyssal

plain.

Parameters Argo Abyssal Plain Gascoyne/Cuvier/Perth

Spreading direction/profile

azimuth:

155 degrees 110 degrees

Spreading full-rate: 100 mm/yr after 136 Ma

70 mm/yr before 136 Ma

70 mm/yr

Axis (ridge) jump: 390 km south at 136 Ma n/a

Depth of the magnetized

layer:

6 km 6 km

Thickness of the

magnetized layer:

0.5 km 0.5 km

Magnetization on (and off)-

axis:

10 A/m 10 A/m

Magnetic field declination: 1 degrees -1 degrees

Magnetic field inclination: -46 degrees -55 degrees

Table 1.2. Parameters used for the Modmag synthetic block models (Gradstein et al.,

1994; Mendel et al., 2005).


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40Ar/39Ar dating of CHRISP samples

Dredging during the August-September 2008 IFM-Geomar CHRISP research cruise in

the Wharton Basin recovered many samples for dating. One sample of volcanic glass,

dredged from the flank of the Investigator Ridge (Fig. 1.1 and 1.3), was found to have a

Jurassic age given the following procedure.

Fresh basalt glass fragments from dredged rock sample SO199-DR-30-1 were

handpicked, crushed, sieved split (250-500µm), washed, and cleaned using an ultrasonic

disintegrator. The glass separate was lined by cadmium foil and irradiated at the 5-MW

reactor of the GKSS Research Center (Helmholtz-Zentrum Geesthacht, Germany). The

neutron flux was monitored using Taylor Creek Rhyolite Sanidine (TCR-2: 27.87 ± 0.04

Ma); (Lanphere and Dalrymple, 2000). 40Ar/39Ar laser step-heating analyses were

carried out using a 20W SpectraPhysics Argon-Ion laser and an MAP 216 series noble

gas mass spectrometer. Argon isotope ratios from mass spectrometry were corrected for

mass discrimination, background and blank values, J-value gradients, and interfering

neutron reactions on Ca and K.


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Figure 1.3. CHRISP EM120 Bathymetry profile along the Investigator Ridge running

north-south along the Wharton Basin. Red star shows the location of the CHRISP 2008

Jurassic sample SO199-DR30, taken from 5060 metres below sea level. Thin black line

shows boundary outlining the limits for the Jurassic sliver interpreted from the

bathymetry profile.

depth (m)


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The step-heating age spectrum (apparent age and error versus cumulative 39Ar) yields a

statistically valid plateau (8 consecutive steps comprising 84% of the 39Ar released, with

ages overlapping within 2Sigma errors), and robust statistics (MSWD = 0.49,

Probability = 0.84). The plateau age, representing the inverse-variance weighted mean

of the plateau step ages and errors, is 153.1 ± 3.3 Ma (2Sigma, including a 0.15% error

in J). Alteration is monitored by calculating the alteration indices, based on the

measured 36Ar/37Ar ratios (Baksi, 2007). Alteration indices of the plateau heating steps

are low (0.0003 – 0.0006) and close to the cut-off values for fresh sample material

suggested by Baksi (2007). Low-temperature heating steps yield significantly higher

alteration indices (up to ~0.5) and are excluded from the plateau. Step-heating results

are shown in combined Age and AI spectra (Fig. 1.4).


22

Figure 1.4. Step-heating age spectrum for the CHRISP sample where the plateau age,

representing the inverse-variance weighted mean of the plateau step ages and errors, is

153.1 ± 3.3 Ma. Alteration indices of the plateau heating steps are low (0.0003 –

0.0006) and close to the cut-off values for fresh sample material suggested by Baksi


23

(2007). Low-temperature heating steps yield significantly higher alteration indices (up

to ~0.5) and are excluded from the plateau.

MAGNETIC ANOMALY INTERPRETATION

We identify two sequences of isochrons in the Argo Abyssal Plain: M26-M21 (155-147

Ma) and M14-M10N (136-131 Ma), becoming younger to the north, (Fig. 1.5 and 1.6),

and two fracture zones from offsets in the magnetic anomalies. Only the older

anomalies are bounded by the fracture zones, in the west and east, the latter having a

much greater offset (about 100 km), mimicking the margin. Our interpretation for the

older anomalies in the Argo Abyssal Plain is in good agreement with previous studies

(Fullerton et al., 1989; Heine and Müller, 2005; Sager et al., 1992). The younger

anomalies (M14-M10) we interpret in the northern Argo Abyssal Plain, are a good

match to a more recent model (Heine and Müller, 2005), (Fig. 1.2b). The M14-M10

anomalies are a better fit to our synthetic model than the M20-M16 anomalies arising

from a continuous sequence (Fullerton et al., 1989, Sager et al., 1992), (Fig. 1.2a). The

northern Argo anomalies have higher magnetic intensities, which also suggests younger

crust. Anomalies M21 and M22, located just south of the M14 (136 Ma) pseudofault

appear attenuated. Over the Joey Rise, an area masked by volcanism, we tentatively

identified chrons M12A-10N (135-131 Ma) trending at 20 degrees, which links the

Argo with the remaining abyssal plains located southwest.


24

Figure 1.5. Marine magnetic anomalies projected at 70 degrees from North for Argo

Abyssal Plain, overlain on 1-minute satellite-derived free-air gravity field. Thin black

lines show marine magnetic anomalies with ship tracks, thick grey lines show the

selected, representative magnetic anomaly profiles shown for Fig. 1.6, thick dashed

black lines show fracture zones, thick solid black lines show pseudofaults and thick

dotted back line shows the COB. Identification of marine magnetic anomalies, picked at

the young end of normal polarity, is shown in the map key.


25

Figure 1.6. Selected, representative magnetic anomaly profiles for the Argo Abyssal

Plain. The location of the profiles is shown in Fig. 1.5. The synthetic profile is based on

the geomagnetic timescale of Cande and Kent (1995), for Cenozoic anomalies, and

Gradstein et al. (1994), for Mesozoic anomalies, using a depth to the top of the

magnetised layer of 6 Km and a thickness of the magnetised layer of 0.5 Km. The

oceanic crust was assumed to have been magnetised at 42 °S.


26

Figure 1.7. Marine magnetic anomalies projected at 20 degrees from North for the

Gascoyne and Cuvier Plains, overlain on 1-minute satellite-derived free-air gravity

field. Thin black lines show marine magnetic anomalies with ship tracks, thick red line

indicates an extinct ridge, thick grey lines show the selected, representative magnetic


27

anomaly profiles shown for Fig. 1.8 and 1.9, thick dashed black lines show fracture

zones, thick solid black lines indicate pseudofaults and thick dotted back line marks the

COB. Identification of marine magnetic anomalies, picked at the young end of normal

polarity, is shown in the map key.


28

Figure 1.8. Selected, representative magnetic anomaly profiles for the Gascoyne

Abyssal Plain. The location of the profiles is shown in Fig. 1.7. The synthetic profile is

based on the geomagnetic timescale of Cande and Kent (1995), for Cenozoic anomalies,

and Gradstein et al. (1994), for Mesozoic anomalies, using a depth to the top of the

magnetised layer of 6 Km and a thickness of the magnetised layer of 0.5 km. The


Figure 1.9. Selected, representative magnetic anomaly profiles for the Cuvier Abyssal

Plain. The location of the profiles is shown in Fig. 1.7. The synthetic profile is based on

the geomagnetic timescale of Cande and Kent (1995), for Cenozoic anomalies, and

Gradstein et al (1994), for Mesozoic anomalies, using a depth to the top of the




29

In the Gascoyne Abyssal Plain, we interpret anomalies M10-M0 (130-120 Ma), as a

continuous sequence trending 20 degrees east from the Exmouth Margin (Fig. 1.7 and

1.8). The anomalies are bisected by a fracture zone, which is just discernable in the

marine gravity grid as faint lineation oriented at roughly 110 degrees, and may be a

westward extension of the CRFZ that is offset slightly to the north. We follow the

magnetic anomaly interpretations featuring Cretaceous seafloor in the Gascoyne

Abyssal Plain (Fullerton et al., 1989; Sager et al., 1992), as opposed to the Jurassic

seafloor of Heine and Müller (2005), Fig. 1.2b, though we cannot identify the conjugate

series M10-M4 (130-126 Ma) by the Exmouth margin (Fullerton et al., 1989; Sager et

al., 1992), Fig. 1.1. Our interpretation differs from that of Robb et al., (2005), because

the geometry and juxtaposition of their interpreted conjugate magnetic anomalies M2

and M4 cannot be accounted for by any reasonable plate motion/ridge propagation

model.

In the Cuvier Abyssal Plain, we identify two sets of conjugate anomalies divided by the

Sonne Ridge, here interpreted as a pseudofault (Fig. 1.7 and 1.9). East of the Sonne

Ridge, we identify anomalies M10-M8 (130.5-128.2 Ma), about an extinct spreading

axis. West of the Sonne Ridge, we identify M6-M4 (127.2-126.7 Ma), reflected about

the Sonja Ridge, a failed propagating ridge, as the anomalies appeared to converge to

the north. Our results differ from previous studies, which identify the Sonne as an

extinct spreading centre surrounded by the conjugate series M10/11-M5 (130/131-126

Ma), (Fullerton et al., 1989, and Mihut and Müller, 1998), though they are similar to

Robb et al., (2005), in having two conjugate sequences. Our results are supported by the


30

different intensity in the marine gravity grid on either side of the Sonne Ridge, and the

character of the CRFZ, which appears to be bisected directly north of the Sonne Ridge.

In the Perth Abyssal Plain, our model (Fig. 1.10 and 1.11) is in agreement with previous

interpretations where chrons M10N (131 Ma) to M0 (124 Ma) are present in the eastern

portion of the basin (Johnson et al., 1980; Markl, 1974, 1978), Fig. 1.2d.

Figure 1.10. Marine magnetic anomalies projected at 20 degrees from North for the

Perth Abyssal Plain, overlain on 1-minute satellite-derived free-air gravity field. Thin

black lines show marine magnetic anomalies with ship tracks, thick grey lines show the

selected, representative magnetic anomaly profiles shown for Fig. 1.11, thick dashed


31

black lines show fracture zones, thick solid black lines show pseudofaults and thick

dotted back line shows the COB. Identification of marine magnetic anomalies, picked at

the young end of normal polarity, is shown in the map key.

Figure 1.11. Selected, representative magnetic anomaly profiles for the Perth Abyssal

Plain. The location of the profiles is shown in Fig. 1.10. The synthetic profile is based

on the geomagnetic timescale of Cande and Kent (1995), for Cenozoic anomalies, and

Gradstein et al. (1994), for Mesozoic anomalies, using a depth to the top of the




32

Our results are in good agreement with all ODP drill site age constraints (Fig. 1.12). The

two drill sites in the Argo Abyssal Plain report Late Jurassic ages. Results from site 261,

in the north-east Argo, reported an age of 152 Ma having Kimmeridgian-Tithonian clay

on a tholeiitic basalt sill overlying basement, to the south, site 765 was dated to 155 Ma

having Tithonian-Berriasian siltstone on pillow basalt (Gradstein, 1992; Veevers et al.,

1974). These are in good agreement with the ages of the magnetic anomalies we

interpreted, site 261 supporting a large sinistral offset in the eastern portion of the Argo

Abyssal Plain. The next oldest drill site, 766, is located near the southwest edge of the

Exmouth Plateau and revealed an oldest date of 130 Ma from Valanginian

sandstone/siltstone overlaying a tholeiitic basalt sill (Gradstein et al., 1992). This site is

just on the oceanic side of our COB and matches well with our modelled onset of

spreading at 136 Ma. At drill site 263, located in the southern portion of the Cuvier

Abyssal Plain, inboard of the Wallaby Plateau, near-basement Albian clay containing

dinoflagellates and nannofossils was dated at 115 Ma (Veevers et al., 1974). While this

is younger than our interpreted age of ~132 Ma, it is allowable given that the sample did

not reach the basement. In the Perth Abyssal Plain, drill site 259, just southeast of the

start of the WZFZ, Neocomian-Aptian claystone overlying a tholeiitic basalt flow was

dated to 112 Ma (Veevers et al., 1974). This is younger than our modelled age of ~124

Ma but is still reasonable given that the sample was not taken from the basement. Drill

sites 260 and 257, in the Gascoyne and Perth Abyssal Plains, respectively, reached mid-

Albian clay near tholeiitic basement and both resulted in minimal seafloor ages of 105

Ma (Davies et al., 1974; Veevers et al., 1974) again, a reasonable match to our modelled

ages of ~126 Ma for site 260 and ~115 Ma for site 257. Site 260 shows the largest age

discrepancy between our interpretation and the drill site ages but we are in agreement

the majority of previous interpretations in that area (e.g. Fullerton et al., 1989; Robb et


33

al., 2005, Sager et al., 1992). Just west of Batavia and Gulden Draak Knolls, and the

CHRISP Jurassic crust, drill site 256 reached Late Albian brown clay (Davies et al.,

1974) and drill site 212 reached basalt basement overlain by brown clay, (Von der

Borch et al., 1974), both reporting minimal ages of ~100 Ma, which is a reasonable

match to our interpreted seafloor ages of 108 and 100 Ma, respectively.

DISCUSSION OF TECTONIC MODEL AND CONSTRAINTS

Mesozoic reconstructions of East Gondwana remain poorly constrained and too tightly

fit, particularly around Madagascar (Lawver et al., 1998; Marks and Tikku, 2001). We

test a new fit-reconstruction for East Gondwana, which shifts the position of Australia,

relative to Antarctica, several hundred kilometres further east than previously modelled

at 83 million years (Williams et al., 2011), creating more accommodation space for the

tectonic blocks. As a result, our blocks have a reasonable fit within Mesozoic East

Gondwana that avoids excessive gaps or overlap. The two main tectonic blocks we

migrate are Argoland and Greater India (including its micro-continental rafts). We have

used all available constraints to define their tectonic outlines and motion, as follows.

The tectonic elements and rotation poles relating to this study can be found in the

supplementary file provided and viewed in GPlates (http://www.gplates.org/index.html).

Argoland extent and motion

New age data from seamounts sampled in the Wharton Basin (Fig. 1.1) during the 2008

CHRISP research cruise add a pivotal constraint to the extents of Argoland and Greater

India. Volcanic glass, dredged from the flanks of the Investigator Ridge (IR, Fig. 1.1),


34

was Ar-Ar dated at 153 ± 3.3 Ma, indicating the presence of a portion of Jurassic

oceanic crust. This finding is striking since Cretaceous seafloor is prevalent in the

abyssal plains inboard of the sample and we would expect this area to have been created

after the inboard abyssal plains. The CHRISP Jurassic seafloor formed coevally to the

seafloor in the Argo Abyssal Plain (from 155 Ma), as an extension of the spreading

ridge between Argoland and Greater India. This new data is therefore instrumental in

defining the southern extent of Argoland and the northern margin of Greater India. We

infer that the Jurassic CHRISP crust originally formed just west of the Zenith Plateau

and was transferred to its present-day position along the prominent curved fracture

zones. The CHRISP Jurassic sliver could not have formed east of the Zenith Plateau, as

it would have permanently joined the Australian plate when the Zenith Plateau was

transferred via a ridge jump, see next section.

We divide Argoland into West, Central and East portions to allow a multi-staged

accretion. The northern margins of all three Argoland blocks are minimum extents and

the width of the slivers varies along strike from 100 km in the east to 500 km in the west

(Fig. 1.13), due to the margin geometry, and the widest portions occur in West and

Central Argoland. West Argoland originally stretched from Africa to the Exmouth

Plateau, it was the longest of the Argoland slivers and was widest at its east. This larger

eastern width is constrained by the geometry of linking the ridge forming the Argo

Abyssal Plain to the CHRISP Jurassic seafloor forming west of the Zenith Plateau (Fig.

1.13b).

The Tethyan Himalayas are considered to have formed from a large area of highly

extended crust forming the northernmost extension of Greater India (e.g. van


35

Hinsbergen et al., 2011). However, greatly extended continental crust is prone to

breakup and subsequent seafloor spreading. The most straightforward way to explain

the provenance of the Tethyan Himalayas is that it actually separated from Greater India

and collided with Eurasia before Greater India. We propose that the Tethyan Himalayas

correspond to West Argoland. The presence of two blocks, divided by a north-northeast

striking boundary reaching the middle of the Lhasa block (Zhang et al., 2007), supports

the combined identity of West Argoland and the Tethyan Himalayas. Central Argoland,

also referred to as the West Burma Block, is wider in the middle because of the curving

geometry of its conjugate, the Argo Abyssal Plain. East Argoland, which stretched from

northeast of the Argo Abyssal Plain to Seram/Birdhead in the west, was conjugate to

Australia’s linear northern margin and we have outlined it as a narrow continental

sliver.

To reconstruct Argoland’s motion, we compute half stage Euler poles and convert them

into full-stage Euler poles given constraints from magnetic anomaly picks and fracture

zones from the Argo Abyssal Plain, including chrons M25-M11 (155-132 Ma). For time

periods where the oceanic crust of the Argo Abyssal Plain has been subducted,

including chrons M20-M15 (146-136 Ma), we maintain a similar rate and direction of

motion for Argoland to that of pre-146 Ma.

Active mid-ocean ridges terminate at strike-slip faults or triple junctions. The spreading

centre forming the Argo Abyssal Plain in the Late Jurassic was likely connected to the

spreading centre in the West Somali Basin as these spreading systems operated during

the same timeframe with compatible spreading configurations. When the Somali ridge

became extinct is contentious with models interpreting extinction at M10 (130 Ma)


36

(Eagles and Konig, 2008; Rabinowitz et al., 1983) or M0 (120 Ma) (Ségoufin and

Patriat, 1980). We prefer the latter model (extinct at 120 Ma) as this links better to the

extinction of the triple junction that temporarily divided Argoland, India and Australia

from 136-120 Ma. During this time, a triple junction would have existed offshore

northeast Africa, separating Africa from India and Argoland. The northern arm of this

triple junction would have been a strike-slip fault between the Western and Central

MesoTethys, so that it could accommodate the separate motions of Argoland relative to

the MesoTethys. The extinction of the active ridge (linking the triple junctions) north of

Greater India around 120 Ma could also explain India’s northward acceleration, (Muller,

2007), reaching ~20 mm/yr (Acton, 1999; Klootwijk et al., 1992; Patriat and Achache,

1984).

Greater India extent and motion

Based on the CHRISP Jurassic age and potential field data offshore West Australia, we

divide Greater India into three distinct portions: 1) the Gascoyne Block, a narrow

indenter sandwiched between West Argoland and the Exmouth Plateau, which created

the Gascoyne Abyssal Plain as it migrated from the Exmouth margin, 2) the Wallaby

and Zenith Plateaus, comprising all the Greater Indian continental material between

CRFZ and WZFZ, these became attached to the Australian plate following two

westward ridge jumps, and 3) the main portion of Greater India, located south of the

WZFZ, which reached roughly 3500 km to the west to meet the margins of Africa and

Madagascar in a Mesozoic full-fit plate reconstruction.


37

We bring the northern extent of Greater India (the Gascoyne Block) inline with the

northern tip of the Exmouth Plateau, a highly extended passive margin, which requires a

conjugate continental flank during rifting. The presence of continental crust west of the

Exmouth Plateau before breakup is supported by seismic stratigraphy in the Rankin

Trend (RT, Fig. 1.1) that reveals a northwest Precambrian sediment source was present

along the northwest shelf during most of the Palaeozoic and Mesozoic (Martison et al.,

1973). We outline the Gascoyne block as a narrow indenter because the ridge forming

the Argo Abyssal Plain reached about 800 km further south, around a slim portion of

Greater India and the potential Exmouth Plateau, to form the CHRISP crust just west of

the Zenith Plateau before its migration. The Gascoyne Block’s northeast margin, which

was conjugate to the Exmouth Plateau, is outlined to match the Australian COB and

allow the coeval oceanic crust, as dated by magnetic anomalies, to form halfway

between the blocks as they separate. The Gascoyne Block’s southern edge was

conjugate to the northwest Wallaby Plateau, to allow complete continental overlap

between itself, West Argoland and Greater India (including the plateaus), in a full-fit

Mesozoic reconstruction (Fig. 1.13a).

For Euler rotations describing the motion of Greater India, including its Gascoyne Block

indenter, we visually fit conjugate magnetic anomaly and fracture zone interpretations

in the Gascoyne, Cuvier and Perth abyssal plains and compute full-stage rotation poles

using GPlates (Boyden et al., 2011). The relative motions between Madagascar and

Africa and Antarctica provide additional constraints for the relative position and motion

of Greater India through time. There are several models available that describe the

initial motion for Africa-Antarctica and Africa-Madagascar. Here we adopt Konig and

Jokat, (2010) and Müller et al., (2008), respectively. To build robust plate tectonic


38

models it is important to consider regional constraints provided by neighbouring plates

to avoid excessive overlap or unlikely motion in regions further afield from the main

area of study. This is particularly significant for the commonly tight fit between

southwest India and Madagascar, which is difficult to resolve without causing overlap

between north India and the WZFZ, which was formed by India’s migration. We avoid

this overlap by fitting Greater India to Madagascar in such a way that it results in less

than 150 km of dextral strike-slip motion between the two plates.

We extend the 136 Ma spreading reorganisation, which formed the northern portion of

the Argo Abyssal Plain and Joey Rise ridges, into a triple junction operating until 120

Ma. The western arm of the triple junction is linked to the African triple junction, where

India’s anticlockwise motion prior to 120 Ma causes minor compression along East

Africa. This is supported by the presence of the Masirah ophiolite of eastern Oman.

Based on the age of potassic granites, the Masirah ophiolite was obducted around 125-

145 Ma (Smewing et al., 1991), inline with a Tithonian age obtained by the analysis of

radiolaria in cherts in the ophiolite (Moseley, 1990), which corresponds to Greater

India’s anticlockwise rotation, from 136-120 Ma. The nucleus of the West Australian

triple junction originated just east of the Joey Rise (Fig. 1.13), though subduction has

ensured there is little evidence remaining for the proposed triple junction, except

possibly for the volcanic Joey and Roo Rises. Its northeast spreading branch was

initiated after a relocation of the NeoTethyan spreading centre to the north Argo

Abyssal Plain, leaving the pseudofault near the Java subduction trench. The southeast

arm began rifting India from Australia, thereby linking the Jurassic and Cretaceous

spreading systems of West Australia.


39

The micro-continental blocks, including Zenith, Wallaby and Naturaliste Plateaus,

Batavia and Gulden Draak Knolls, share the same Euler poles as Greater India until they

are transferred to the Australian plate by localised ridge jumps. We date these ridge

jumps using our magnetic anomaly interpretations and/or interpolation of India-

Australia spreading rates to: Wallaby Plateau ~128 Ma, Naturaliste and West Wallaby

Plateau ~127 Ma, Zenith Plateau ~124 Ma (along with the CHRISP Jurassic seafloor),

Batavia and Gulden Draak Knolls ~108 Ma (transferring the CHRISP Jurassic seafloor

back to the Indian plate). Throughout the CNS, we maintain a steady spreading rate for

Greater India that compares with spreading rates before and after that time. However,

India’s motion alters ~99 Ma to satisfy the change in transform fault azimuths in the

Wharton Basin as India began to migrate north instead of northwest, ultimately resulting

in the curved fracture zones visible today. The onset of spreading between India and

Madagascar has commonly been dated as around 85 Ma (Storey et al., 1995; Yatheesh

et al., 2006); our model initiates this separation with ~200 km of dextral strike-slip

motion from ~99 Ma followed by seafloor spreading from ~94 Ma, progressing from

south to north (Gibbons et al., in prep). The timing of this separation fits well with a

major spreading reorganisation identified in the Indian Ocean ~100 Ma (Müller et al.,

2000; Veevers, 2000), and the emplacement of the Androy and Morondava basalts on

Madagascar’s east and west margins from 103 and 94 Ma, respectively (Bardintzeff et

al., 2010). As this new spreading regime was established, the CHRISP Jurassic seafloor

was attached to the Investigator ridge via a minor spreading reorganisation ~99 Ma.


40

Tectonic model

The West Australian margin began forming at ~155 Ma, with the onset of seafloor

spreading along the Argo Ridge. The ridge likely linked to a triple junction offshore

Somalia (west), having originated from East Timor. Spreading about this ridge caused

the northward migration of Argoland, creating the Argo Abyssal Plain and CHRISP

Jurassic crust (Fig. 1.13b). Argoland continued migrating north but its spreading system

underwent a reorganisation at 136 Ma, forming a new, steeper arm along the north Argo

Abyssal Plain pseudofault, roughly 800 km further south of the old Argo spreading

ridge at this time, (Fig. 1.6 and Fig. 1.13c). This new portion of the ridge reached

around the entire West Australian margin, forming the triple junction whose nucleus

was located between the Joey and Roo Rises (Fig. 1.13c). Separation between India and

Australia followed, with the formation of the Australian western margin abyssal plains.

Greater India and its northern indenter, the Gascoyne Block, began migrating from the

West Australian margin in an anticlockwise motion as the new spreading centre

propagated south from the Exmouth Plateau after the 136 Ma spreading reorganisation.

This is close to the onset of seafloor spreading between India and East Antarctica at 130

Ma (chron M9) (Gaina et al., 2007), and the ~6 million year discrepancy is reasonable

given the initial anticlockwise motion for Greater India about its southern pivot. India’s

anticlockwise motion is a vital component in our model to avoid overlap between

India’s southwest margin and Madagascar, and India’s northeast margin and the WZFZ.

As a result, spreading rates were higher in the northern part of the Western Australian

abyssal plains, with the maximum rates presumably at the Joey Rise volcanic province,

where the triple junction nexus was located. From 136 Ma, the Exmouth margin


41

underwent crustal stretching while the Joey Rise ridges formed at its north. These

volcanic ridges have been attributed to magma concentrated in crustal drainage channels

beneath the underplated Exmouth plateau, (Frey et al., 1998), or as failed rifts (Direen et

al., 2008), but the presence of sills connecting the Joey Rise to the Exmouth Plateau

(Heirtzler et al., 1978) support our interpretation that both formed concurrently. The

West Australian margin was formed in the following sequence: Perth margin from ~136

Ma, the Gascoyne margin from ~135 Ma and the Cuvier margin from ~133 Ma. This

unusual age progression is due to our allocated boundaries for the blocks, as discussed

earlier.

From 136 Ma to 100 Ma, Greater India continued its westward migration, leaving

several micro-continental blocks behind via ridge jumps. The first ridge jump occurred

in the Cuvier Abyssal Plain ~128 Ma, transferring the Wallaby Plateau to the Australian

Plate, trapping the older conjugate anomalies inboard of the Sonne Ridge and

introducing an offset in the middle of the CRFZ at the northern tip of the Sonne Ridge

(Fig. 1.12). The Naturaliste Plateau continental crust was stretched until ~127 Ma and

our plate reconstruction accurately models the formation of the Leeuwin Fracture Zone

located between the Naturaliste and the Southwest Australian margin and its conjugate,

the Vincennes fracture zone located east of the Bruce Rise on the Antarctic margin. The

second westward ridge jump, at roughly 127 Ma, transferred the West Wallaby Plateau

to the Australian plate. Between the West and East Wallaby Plateau, the Sonja Ridge is

the extinct ridge, or failed rift system, that corresponds to this second westward ridge

jump. The third westward ridge jump, at around 124 Ma, transferred the Zenith Plateau

and CHRISP Jurassic sliver to the Australian plate.


42

Figure 1.12. Location of isochrons (age-coded: M25, orange; M24, blue; M22A,

magenta; M13, light blue; M11A, grey; M10N, lilac; M6, apricot; M4, yellow; M2,

green; M0, black), marine magnetic anomaly picks at young end of normal polarity

(black dots), pseudofaults (black and white lines), extinct ridges (yellow lines),

continental rafts as outlined by the COB (purple dashed line), interpreted in this study

along the Western Australian margin, overlain on 1-minute satellite-derived free-air


43

gravity field. Red stars are the locations of ODP/DPSP drill sites relevant to this study.

Abbreviations are same as in Fig. 1.

The CHRISP Jurassic sliver (C, Fig. 1.13d) remained west of the Zenith Plateau from

124 Ma until a fourth ridge jump, at 108 Ma, attached Batavia and Gulden Draak Knolls

to the Australian plate (B and G, Fig. 1.13e), and the CHRISP Jurassic sliver to the

Indian plate (C, Fig. 1.13e). Two ridge jumps in opposing directions in adjacent

spreading corridors are modelled to satisfy key observations: south of the WZFZ a

westward ridge jump is required to attach Batavia and Gulden Draak Knolls to the

Australian plate, while north of the WZFZ an eastward ridge jump is required to attach

the CHRISP Jurassic sliver back to the Indian plate so that it can be transferred to its

present day location on the Investigator Ridge. This ridge jump also left an extinct

spreading centre in the middle of the Perth Abyssal Plain and presumably a conjugate

sequence of Mesozoic anomalies in the western portion, though the area is heavily

influenced by volcanism and a lack of magnetic anomaly tracks. We interpret Dirk

Hartog Ridge as this extinct spreading centre. This interpretation matches a continuous

spreading rate of roughly 70 mm/yr from 126.7-108 Ma with about 10% faster

spreading rates on the Australian flank, given the amount of seafloor produced in that

time. This >700 km westward relocation for the spreading centre at 108 Ma was likely a

ridge-hotspot induced ridge jump (Mittelstaedt et al., 2008), towards the Kerguelen

Plume, which was located about 300 km directly south of Gulden Draak Knoll at the

time (Fig. 1.13e).


44

Figure 1.13. Mercator-projected reconstructions of the West Australian margin at (a)

200 Ma, (b) 150 Ma, (c) 130 Ma and (d) 120 Ma (e) 100 Ma, (f) 90 Ma, constructed

using GPlates exported geometries with Australia fixed in present-day coordinates.

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45

Showing pseudofaults (green dashed lines), extinct ridges (blue dashed lines), COB

(thin black line, continental side filled in yellow), isochrons (red lines), spreading

centres (brown dashed lines). Yellow polygons indicate continental micro-fragments,

coastlines are filled in grey and large igneous provinces are shown in red. Abbreviations

include Argo Abyssal Plain (AAP), Batavia Knoll (B), CHRISP Jurassic sliver (C, not

drawn to scale), Elan Bank (EB), Cuvier Abyssal Plain (CAP), Gascoyne Abyssal Plain

(GAP), Gulden Draak Knoll (G), Kerguelen plume (K), Perth Abyssal Plain (PAP),

Exmouth Plateau (EP), Naturaliste Plateau (NP), Wallaby Plateau (WP) and Zenith

Plateau (ZP).

The Dirk Hartog Ridge is a linear feature mimicking the margin orientation and it is

linked along its northern limit to the Gulden Draak and Batavia Knolls via the Lost

Dutchmen Ridge. The crustal nature of the knolls is unknown as they have not been

dredged, but they could be continental rafts, or else associated with ridge propagation

events (extinct ridges and pseudofaults) and Kerguelen volcanism. We incorporated

Batavia and Gulden Draak Knolls into our model as tectonic blocks with continental

cores, as the 108 Ma ridge jump in the Perth Abyssal Plain conserves a reasonable COB

overlap (50-300 km) in a Mesozoic full-fit reconstruction (Fig. 1.13a), where the Knolls

fitted well about the western edge of the Naturaliste Plateau.

The anomalous Wallaby-Zenith and Wharton Basin fracture zones

Our model accurately reconstructs the unusual width and morphology of the WZFZ,

which was originally composed of three major east-west trending fracture zones. We

also identify the en-echelon offset ridges in the marine gravity grid, oriented southwest


46

from the base of the Wallaby, and agree with Nelson et al., (2009) that they were

formed gradually under a transtensional regime. We model the en-echelon fracture

zones as forming from ~110 Ma, bifurcating the original Wallaby-Zenith fracture zones

as Greater India underwent a slight southward motion just prior to the 108 Ma ridge

jump. This process can be seen in the curved fracture zones directly west of the southern

Zenith Plateau. This transtensional motion could also be responsible for creating Lost

Dutchmen Ridge via a leaky transform, west of the WZFZ, where the en echelon

fracture zones are not observed. This leaky transform (Lost Dutchmen Ridge) may have

extended to the Perth spreading centre (Dirk Hartog Ridge), which was to become

extinct at 108 Ma, and may have contributed to its volcanic appearance as seen in the

marine gravity grid.

This is the first study to reproduce the trace of the Wharton Basin curved fracture zones

in a tectonic reconstruction model. The curved fracture zones are only found west of the

Zenith Plateau so their prominence may be related to the presence of the older/colder

CHRISP Jurassic oceanic crust, when the ridge initiated spreading between the CHRISP

Jurassic seafloor and the Zenith Plateau at 108 Ma. The seafloor south of the curving

fracture zones formed closer to the Kerguelen hotspot, where warmer mantle may have

resulted in ocean floor with a smoother morphology. The seafloor northwest of the

Zenith Plateau is also smooth but this area did not experience a ridge jump at 108 Ma.

We propose that the curved fracture zones were a manifestation of the eastward ridge

jump that transferred the Jurassic CHRISP crust back to the Indian plate at 108 Ma, as

well as a continuation of the WZFZ.


47

CONCLUSIONS

We derive a comprehensive regional tectonic model that can account for all major

tectonic features visible in the marine gravity grid off the West Australian margin.

These include volcanic ridges, submerged plateaus/continental rafts, the CHRISP

Jurassic sliver, and fracture zones including the complex morphology of the WZFZ and

those curving in the Wharton Basin, coinciding with the 100 Ma spreading

reorganisation. Our plate tectonic model satisfies the potential field and ODP/CHRISP

age data, yet remains relatively simple and provides a complete scenario for the early

formation of the eastern Indian Ocean. The CHRISP Jurassic seafloor provides essential

new insights into the original extents of Argoland and Greater India so that the major

extent of Greater India lay south of the WZFZ in a Mesozoic West Australian margin

reconstruction. North of the WZFZ, Argoland must have extended hundreds of km

further west to the east African margin but, to form the CHRISP Jurassic seafloor so

that it could be emplaced where it is today, the spreading centre migrating Argoland

from Greater India veered around the margin that later became the Exmouth Plateau.

This ridge configuration reduced the portion of northern Greater India north of the

WZFZ, also conjugate to the Exmouth and Wallaby Plateaus, to an indenter roughly 750

km long by 100 km wide, which we call the Gascoyne Block. Our model links the

Jurassic and Cretaceous spreading episodes from the rifting of Argoland and Greater

India, respectively, via a spreading reorganisation at ~136 Ma. From which time, a triple

junction operated between Argoland, India and Australia, in order to avoid applying

India’s initial anticlockwise rotation to Argoland. The northwest Australian triple

junction linked to an East African triple junction but both triple junctions became

extinct around 120 Ma when Argoland and India were attached to the same pole of


48

rotation. The Early Cretaceous migration of Greater India formed West Australia’s

abyssal Plains, including the Gascoyne Abyssal Plain, which was formed by the

migration of its northern indenter, the Gascoyne Block. The Cuvier and Perth Abyssal

Plains became bounded by continental crust following ridge jumps isolating the Zenith

and Wallaby Plateaus, and Batavia and Gulden Draak Knolls, respectively, though this

occurred several million years earlier for the northern abyssal plain.


49

REFERENCES

Acton, G., 1999, Apparent Polar Wander of India Since the Cretaceous with Implications for Regional Tectonics and True Polar Wander: Memoir Geological Society of India, v. 44, p. 129-175.

Aitchison, J.C., Ali, J.R., and Davis, A.M., 2007, When and where did India and Asia collide?: Journal of Geophysical Research-Solid Earth, v. 112.

Aitchison, J.C., and Davis, A.M., 2004, Evidence for the multiphase nature of the India-Asia collision from the Yarlung Tsangpo suture zone, Tibet: Aspects of the Tectonic Evolution of China, v. 226, p. 217-233.

Ali, J.R., and Aitchison, J.C., 2005, Greater India: Earth-Science Reviews, v. 72, p. 169-188.

Baksi, A.K., 2007, A quantitative tool for detecting alteration in undisturbed rocks and minerals - I: Water, chemical weathering, and atmospheric argon.: Geological Society of America Special Paper 430, p. p. 285-303.

Bardintzeff, J.M., Liegeois, J.P., Bonin, B., Bellon, H., and Rasamimanana, G., 2010, Madagascar volcanic provinces linked to the Gondwana break-up: Geochemical and isotopic evidences for contrasting mantle sources: Gondwana Research, v. 18, p. 295-314.

Besse, J., and Courtillot, V., 2002, Apparent and true polar wander and the geometry of the geomagnetic field over the last 200 Myr - art. no. 2300: Journal of Geophysical Research-Solid Earth, v. 107, p. 2300-2300.

Borissova, I., 2002, Geological framework of the Naturaliste Plateau: Geoscience Australia Record 2002/20.

Brown, B.J., Muller, R.D., C., G., Struckmeyer, H.I.M., Stagg, H.M.J., and Symonds, P., 2003, Formation and evolution of Australian passive margins: implications for locating the boundary between continental and oceanic crust: Geol. Soc. Australia Spec. Publ. 22, and Geol. Soc. America Spec. Pap. 372, p. 223-243.

Cande, C., and Stegman, D.R., 2011, Indian and African plate motions driven by the push force of the Reunion plume head: Nature, v. 475.

Cande, S.C., and Kent, D.V., 1995, Revised calibration of the geomagnetic polarity timescale for the Late Cretaceous and Cenozoic: Journal of Geophysical Research, v. 100, p. 6093-6095.

Chen, J.S., Huang, B.C., and Sun, L.S., 2010, New constraints to the onset of the India-Asia collision: Paleomagnetic reconnaissance on the Linzizong Group in the Lhasa Block, China: Tectonophysics, v. 489, p. 189-209.

Davies, T.A., Luydendyk, B.P., Rodolfo, K.S., Kempe, D.R.C., MvKelvey, R.D., Leidy, R.D., Horvath, G.J., Hyndman, R.D., Thierstein, H.R., Herb, R.C., Boltovskoy, E., and Doyle, P., 1974, Init. Repts.of DSDP: Washington, D.C., DSDP.


50

Ding, L., Kapp, P., and Wan, X.Q., 2005, Paleocene-Eocene record of ophiolite obduction and initial India-Asia collision, south central Tibet - art. no. TC3001: Tectonics, v. 24, p. C3001-C3001.

Direen, N.G., Stagg, H.M.J., Symonds, P.A., and Colwell, J.B., 2008, Architecture of volcanic rifted margins: new insights from the Exmouth-Gascoyne margin, Western Australia: Aust J Earth Sci, v. 55, p. 341-363.

Dupont-Nivet, G., Lippert, P.C., van Hinsbergen, D.J.J., Meijers, M.J.M., and Kapp, P., 2010, Palaeolatitude and age of the Indo-Asia collision: palaeomagnetic constraints: Geophysical Journal International, v. 182, p. 1189-1198.

Eagles, G., and Konig, M., 2008, A model of plate kinematics in Gondwana breakup: Geophysical Journal International, v. 173, p. 703-717.

Falvey, D.A., 1972, Sea Floor Spreading in the Wharton Basin (Northeast Indian Ocean) and the Breakup of Eastern Gondwanaland: Australian Petroleum Exploration Association, v. 12, p. 2.

Falvey, D.A., and Veevers, J.J., 1974, Physiography of the Exmouth and Scott Plateaux, western Australia, and adjacent northeast Warton Basin: Mar. Geol., v. 17, p. 21-59.

Frey, O., Planke, S., Symonds, P.A., and Heeremans, M., 1998, Deep crustal structure and rheology of the Gascoyne volcanic margin, western Australia: Mar Geophys Res, v. 20, p. 293-312.

Fullerton, L.G., Sager, W.W., and Handschumacher, D.W., 1989, Late Jurassic-Early Cretaceous evolution of the eastern Indian Ocean adjacent to northwest Australia: Journal of Geophysical Research, v. 94, p. 2937-2953.

Gaina, C., Müller, R.D., Brown, B., Ishihara, T., and Ivanov, S., 2007, Breakup and early seafloor spreading between India and Antarctica Journal of Geophysics International, v. 170, p. 151-170.

Gibbons, A.D., Whittaker, J., and Dietmar Muller, R., in prep, A regional tectonic model for the Enderby Basin, East Antarctica, suggests a later breakup between India and Antarctica but an earlier breakup for India and Madagascar.

Gradstein, F.M., 1992, Leg 122-123, northwestern Australian margin; a stratigraphic and paleogeographic summary, in Gradstein Felix, M., Ludden John, N., Adamson Andrew, C., Baumgartner Peter, O., Beausillon, R., Bolmer, S.T., Bown Paul, R., Brereton, N.R., Buffler Richard, T., Castillo David, A., Compton John, S., Dumoulin Julie, A., Griffiths Cedric, M., Haig, D., Heggie David, T., Ishiwatari, A., Kaminski Michael, A., Kodama, K., Kopaska Merkel David, C., Marcoux Jean, P., McMinn, A., Moran Michael, J., Mutterlose, J., Ogg James, G., Brennan, O.N., Plank, T., Riggins, M., Schott, M., Simmons Gregory, R., Thurow, J., Stewart Sondra, K., Kennett Diana, M., and Mazzullo Elsa, K., eds., Proceedings of the Ocean Drilling Program, Argo abyssal plain/ Exmouth Plateau; covering Leg 123 of the cruises of the drilling vessel JOIDES


51

Resolution, Singapore, Republic of Sing., to Singapore, Republic of Sing., sites 765-766, 28 August 1988-1 November 1988., Volume 123: Proceedings of the Ocean Drilling Program, Scientific Results: College Station, TX, United States, Texas A & M University, Ocean Drilling Program, p. 801-816.

Gradstein, F.M., Agterberg, F.P., Ogg, J.G., Hardenbol, J., van Veen, P., Thierry, J., and Huang, Z., 1994, A Mesozoic time scale: Journal of Geophysical Research, v. 99, p. 24,051-24,074.

Heezen, B.C., and Tharp, M., 1965, Physiographic diagram of the Indian Ocean (with descriptive sheet): New-York.

Heine, C., and Müller, R.D., 2005, Late Jurassic rifting along the Australian Northwest Shelf: margin geometry and spreading ridge configuration: Australian Journal of Earth Science, v. 52, p. 27-39.

Heirtzler, J.R., Cameron, P., Cook, P.J., Powell, T., Roeser, H.A., Sukardi, S., and Veevers, J.J., 1978, The Argo Abyssal Plain: Earth and Planetary Science Letters, v. 41, p. 21-31.

Hirn, A., 1988, Features of the Crust Mantle Structure of Himalayas Tibet - a Comparison with Seismic Traverses of Alpine, Pyrenean and Variscan Orogenic Belts: Philosophical Transactions of the Royal Society of London Series a-Mathematical Physical and Engineering Sciences, v. 326, p. 17-32.

Johnson, B.D., Powell, C.M., and Veevers, J.J., 1980, Early spreading history of the Indian Ocean between India and Australia: Earth and Planetary Science Letters, v. 47, p. 131-143.

Johnson, M.R.W., 2002, Shortening budgets and the role of continental subduction during the India-Asia collision: Earth-Science Reviews, v. 59, p. 101-123.

Klootwijk, C.T., Gee, J.S., Peirce, J.W., Smith, G.M., and McFadden, P.L., 1992, An early India-Asia contact: Paleomagnetic constraints from Ninetyeast Ridge, ODP Leg 121: Geology, v. 20, p. 395-398.

Klootwijk, C.T., Gee, J.S., Peirce, J.W., Smith, G.M., Weissel, J.K., Taylor, E., Dehn, J., Driscoll, N.W., Farrell, J.W., Fourtanier, E., Frey, F.A., Gamson, P.D., Gibson, I.L., Janecek, T.R., Klootwijk, C.T., Lawrence, J.R., Littke, R., Newman, J.S., Nomura, R., Owen, R.M., Pospichal, J.J., Rea, D.K., Resiwati, P., Saunders, A.D., Smit, J., Tamaki, K., Weis, D., and Wilkinson, C., 1991, Constraints on the India-Asia convergence; paleomagnetic results from Ninetyeast Ridge: Proceedings of the Ocean Drilling Program, Scientific Results, v. 121, p. 777-882.

Konig, M., and Jokat, W., 2010, Advanced insights into magmatism and volcanism of the Mozambique Ridge and Mozambique Basin in the view of new potential field data: Geophysical Journal International, v. 180, p. 158-180.


52

Lanphere, M.A., and Dalrymple, G.B., 2000, First-principles calibration of 38Ar tracers: Implications for the ages of 40Ar/39Ar fluence monitors.: U.S. Geological Survey Professional Paper 1621, 10p.

Lawver, L.A., Gahagan, L.M., and Dalziel, I.W.D., 1998, A Tight Fit - Early Mesozoic Gondwana, A Plate Reconstruction Perspective: Memoirs of the National Institute of Polar Research, Special Issue, v. 53, p. 214-229.

Lee, T.-Y., and Lawver, L.A., 1995, Cenozoic plate reconstruction of Southeast Asia: Tectonophysics, v. 251, p. 85-138.

Li, Q., Gao, R., Lu, Z., Guan, Y., Zhang, J., Li, P., Wang, H., He, R., and Karplus, M., 2009, The thickness and structural characteristics of the crust across Tibetan plateau from active-sources seismic profiles: Earthquake Science, v. 22, p. 21-31.

Liebke, U., Appel, E., Ding, L., Neumann, U., Antolin, B., and Xu, Q.A., 2010, Position of the Lhasa terrane prior to India-Asia collision derived from palaeomagnetic inclinations of 53 Ma old dykes of the Linzhou Basin: constraints on the age of collision and post-collisional shortening within the Tibetan Plateau: Geophysical Journal International, v. 182, p. 1199-1215.

Markl, R.G., 1974, Evidence for the breakup of eastern Gondwanaland by the Early Cretaceous: Nature, v. 251, p. 196-200.

—, 1978, Evidence for the early Cretaceous breakup of Gondwanaland off southwestern Australia: Marine Geology, v. 26, p. 41-48.

Marks, K.M., and Tikku, A.A., 2001, Cretaceous reconstructions of East Antarctica, Africa and Madagascar: Earth & Planetary Science Letters, v. 186, p. 479-495.

Martison, N.W., Mcdonald, D.R., and Kaye, P., 1973, Exploration on Continental-Shelf Off Northwest Australia: American Association of Petroleum Geologists Bulletin, v. 57, p. 972-989.

McKenzie, D., and Sclater, J.G., 1971, The evolution of the Indian Ocean since the Late Cretaceous: Geophys. J. R. astr. Soc., v. 24, p. 437-528.

Mendel, V., Munschy, M., and Sauter, D., 2005, MODMAG, a MATLAB program to model marine magnetic anomalies: Computers & Geosciences, v. 31, p. 589–597

Metcalfe, I., 1996, Gondwanaland Dispersion, Asian Accretion and Evolution of Eastern Tethys: Australian Journal of Earth Sciences, v. 43, p. 605-623.

Mihut, D., and Muller, R.D., 1998, Volcanic Margin Formation and Mesozoic Rift Propagators in the Cuvier Abyssal Plain Off Western Australia: Journal of Geophysical Research-Solid Earth, v. 103, p. 27135-27149.

Mittelstaedt, E., Ito, G., and Behn, M.D., 2008, Mid-ocean ridge jumps associated with hotspot magmatism: Earth Planet Sci Lett, v. 266, p. 256-270.


53

Molnar, P., and Tapponnier, P., 1975, Cenozoic tectonics of Asia; effects of a continental collision: Science, v. 189, p. 419-426.

Moseley, F., 1990, The Structure of Masirah Island, Oman: Geology and Tectonics of the Oman Region, v. 49, p. 665-671.

Muller, R.D., 2007, Earth science - An Indian cheetah: Nature, v. 449, p. 795-797.

Müller, R.D., Gaina, C., Tikku, A., Mihut, D., Cande, S., and Stock, J.M., 2000, Mesozoic/Cenozoic tectonic events around Australia, in Richards, M., and Gordon, R., eds., The History and Dynamics of Global Plate Motions, Volume 121: American Geophysical Union Monograph, American Geophysical Union, p. 161-188.

Müller, R.D., Goncharov, A., and Kritski, A., 2005, Geophysical evaluation of the enigmatic Bedout basement high, offshore northwestern Australia: Earth and Planetary Science Letters, v. 237, p. 264-284.

Müller, R.D., Sdrolias, M., Gaina, C., and Roest, W.R., 2008, Age, spreading rates and spreading asymmetry of the world's ocean crust: Geochemistry, Geophysics, Geosystems, v. 9, p. Q04006, doi:10.1029/2007GC001743

Nelson, G., Hughes, M., Przeslawski, R., Nichol, S., Lewis, B., and Rawsthorn, K., 2009, Revealing the Wallaby Plateau - Recent survey delivers geophysical, geological and biophysical data: AusgeoNews, p. 1-4.

Norton, I.O., and Sclater, J.G., 1979, A model for the evolution of the Indian Ocean and the breakup of Gondwanaland: Journal of Geophysical Research, v. 84, p. 6803-6830.

Patriat, P., and Achache, J., 1984, India-Eurasia collision chronology has implications for crustal shortening and driving mechanisms of plates: Nature, v. 311, p. 615-621.

Powell, C.M., Roots, S.R., and Veevers, J.J., 1988, Pre-breakup continental extension in East Gondwanaland and the early opening of the eastern Indian Ocean: Tectonophysics, v. 155, p. 261-283.

Powell, T.S., and Luyendyk, B.P., 1982, The seafloor spreading history of the eastern Indian Ocean: Marine Geophysical Researches, v. 5, p. 225-247.

Rabinowitz, P.D., Coffin, M.F., and Falvey, D., 1983, The separation of Madagascar and Africa: Science, v. 220, p. 67-69.

Ratschbacher, L., Frisch, W., Liu, G.H., and Chen, C.S., 1994, Distributed Deformation in Southern and Western Tibet during and after the India-Asia Collision: Journal of Geophysical Research-Solid Earth, v. 99, p. 19917-19945.

Rey, S.S., Planke, S., Symonds, P.A., and Faleide, J.I., 2008, Seismic volcano stratigraphy of the Gascoyne Margin, Western Australia: J Volcanol Geotherm Res, v. 172, p. 112-131.


54

Robb, M.S., Taylor, B., and Goodliffe, A.M., 2005, Re-examination of the magnetic lineations of the Gascoyne and Cuvier Abyssal Plains, off NW Australia Geophysical Journal International, v. 163, p. 42-55.

Sager, W.W., Fullerton, L.G., Buffler, R.T., and Handschumacher, D.W., 1992, Argo Abyssal Plain magnetic lineations revisited: implications for the onset of seafloor spreading and tectonic evolution of the eastern Indian Ocean, Proceedings of the ODP., Scientific Results, Volume 123: College Station, Texas, ODP.

Sandwell, D.T., and Smith, W.H.F., 2009, Global marine gravity from retracked Geosat and ERS-1 altimetry: Ridge segmentation versus spreading rate: Journal of Geophysical Research-Solid Earth, v. 114.

Schlich, R., 1982, The Indian Ocean: aseismic ridges, spreading centers and oceanic basins, in Nairn, A., and Stehli, F., eds., The Ocean Basins and Margins, Volume 6: New York, Plenum, p. 51-147.

Sclater, J.G., and Fisher, R.L., 1974, Evolution of the east central Indian Ocean, with emphasis on the tectonic setting of the Ninetyeast Ridge: Geological Society of America Bulletin, v. 85, p. 683-702.

Searle, M.P., Windley, B.F., Coward, M.P., Cooper, D.J.W., Rex, A.J., Rex, D., Li, T.D., Xiao, X.C., Jan, M.Q., Thakur, V.C., and Kumar, S., 1987, The Closing of Tethys and the Tectonics of the Himalaya: Geological Society of America Bulletin, v. 98, p. 678-701.

Ségoufin, J., and Patriat, P., 1980, Existence d'anomalies mésozoïques dans le bassin de Somalie. Implications pour les relations Afrique-Antarctique-Madagascar: C. R. Acad. Sci. Paris, v. 291, p. 85-88.

Shi, X.Y., Yin, J.R., and Jia, C.P., 1996, Mesozoic to Cenozoic sequence stratigraphy and sea-level changes in the Northern Himalayas, Southern Tibet, China: Newsletters on Stratigraphy, v. 33, p. 15-61.

Smewing, J.D., Abbotts, I.L., Dunne, L.A., and Rex, D.C., 1991, Formation and Emplacement Ages of the Masirah Ophiolite, Sultanate of Oman: Geology, v. 19, p. 453-456.

Stilwell, J.D., Quilty, P.G., and Mantle, D.J., 2012, Paleontology of Early Cretaceous deep-water samples dredged from the Wallaby Plateau: new perspectives of Gondwana break-up along the Western Australian margin: Australian Journal of Earth Sciences: An International Geoscience Journal of the Geological Society of Australia, v. 59, p. 29-49.

Storey, M., Mahoney, J.J., Saunders, A.D., Duncan, R.A., Kelley, S.P., and Coffin, M.F., 1995, Timing of hot spot-related volcanism and the breakup of Madagascar and India: Science, v. 267, p. 852-855.


55

Sun, Z.M., Jiang, W., Li, H.B., Pei, J.L., and Zhu, Z.M., 2010, New paleomagnetic results of Paleocene volcanic rocks from the Lhasa block: Tectonic implications for the collision of India and Asia: Tectonophysics, v. 490, p. 257-266.

Symonds, P.A., Planke, S., Frey, O., and Skogseid, J., 1998, Volcanic evolution of the Western Australian continental margin and its implications for basin devlopement, in Purcell, P.G.R.R., ed., The sedimentery basins of Western Australia 2: Proceedings of the PESA Symposium., Petroleum Exploration Society, Perth, p. 33-54.

Tan, X.D., Gilder, S., Kodama, K.P., Jiang, W., Han, Y.L., Zhang, H., Xu, H.H., and Zhou, D., 2010, New paleomagnetic results from the Lhasa block: Revised estimation of latitudinal shortening across Tibet and implications for dating the India-Asia collision: Earth Planet Sci Lett, v. 293, p. 396-404.

Teng, J.W., 1987, Explosion Study of the Structure and Seismic Velocity Distribution of the Crust and Upper Mantle under the Xizang (Tibet) Plateau: Geophysical Journal of the Royal Astronomical Society, v. 89, p. 405-414.

Torsvik, T., Müller, R.D., Van der Voo, R., Steinberger, B., and Gaina, C., 2008, Global Plate Motion Frames: Toward a unified model: Reviews in Geophysics, v. in press.

van Hinsbergen, D.J.J., Steinberger, B., doubrovine, P.V., and Gassmoller, R., 2011, Acceleration and deceleration of India-‐Asia convergence since the Cretaceous: Roles of mantle plumes and continental collision: Journal of Geophysical Research, v. 116.

Veevers, J.J., 2000, Change of tectono-stratigraphic regime in the Australian plate during the 99 Ma (mid-Cretaceous) and 43 Ma (mid-Eocene) swerves of the Pacific: Geology, v. 28, p. 47-50.

Veevers, J.J., Heirtzler, J.R., and al., e., 1974, Leg XXVII, Initial Reports of the Deep Sea Drilling Project: Washington, U.S. Govt. Printing Office.

Veevers, J.J., Powell, C.M., and Roots, S.R., 1991, Review of seafloor spreading around Australia. I. Synthesis of the patterns of spreading: Australian Journal of Earth Sciences, v. 38, p. 373-389.

von Stackelberg, U., Exon, N.F., von Rad, U., Quilty, P., Shafik, S., Beiersdorf, H., Seibertz, E., and Veevers, J.J., 1980, Geology of the Exmouth and Wallaby plateaus off northwest Australia: sampling of seismic sequences: Journal of Australian Geology and Geophysics, v. 5, p. 113-140.

Wang, Q., Zhang, P.Z., Freymueller, J.T., Bilham, R., Larson, K.M., Lai, X., You, X.Z., Niu, Z.J., Wu, J.C., Li, Y.X., Liu, J.N., Yang, Z.Q., and Chen, Q.Z., 2001, Present-day crustal deformation in China constrained by global positioning system measurements: Science, v. 294, p. 574-577.


56

Willems, H., Zhou, Z., Zhang, B., and Grafe, K.-U., 1996, Stratigraphy of the Upper Cretaceous and Lower Tertiary strata in the Tethyan Himalayas of Tibet (Tingri area, China): Geol. Rundsch, v. 85, p. 723-754.

Williams, S.E., Whittaker, J., and Müller, R.D., 2011, Full-fit, palinspastic reconstruction of the conjugate Australian-Antarctic margins: Tectonics (submitted).

Yatheesh, V., Bhattacharya, G.C., and Mahender, K., 2006, The terrace like feature in the mid-continental slope region off Trivandrum and a plausible model for India-Madagascar juxtaposition in immediate pre-drift scenario: Gondwana Research, v. 10, p. 179-185.

Yin, A., and Harrison, T.M., 2000, Geologic evolution of the Himalayan-Tibetan orogen: Annual Review of Earth and Planetary Sciences, v. 28, p. 211-280.

Zhang, X.M., Sun, R.M., and Teng, J.W., 2007, Study on crustal, lithospheric and asthenospheric thickness beneath the Qinghai-Tibet Plateau and its adjacent areas: Chinese Science Bulletin, v. 52, p. 797-804.

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